The embodiments of the present invention relate generally to a system and method of operating an engine and, more specifically, to a system and method for controlling exhaust emissions of an engine.
Compression-ignition engines, such as diesel engines, operate by directly injecting a fuel (e.g., diesel fuel) into compressed air in one or more piston-cylinder assemblies, such that the heat of the compressed air ignites the fuel-air mixture. Compression-ignition engines may also include a glow plug to provide heat to ensure ignition. The direct fuel injection atomizes the fuel into droplets, which evaporate and mix with the compressed air in the combustion chambers of the piston-cylinder assemblies. Typically, compression-ignition engines operate at a relatively higher compression ratio than spark ignition engines. The compression ratio directly affects the engine performance, efficiency, exhaust pollutants, and other engine characteristics. In addition, the fuel-air ratio affects engine performance, efficiency, exhaust pollutants, and other engine characteristics. Exhaust emissions generally include pollutants such as carbon oxides (e.g., carbon monoxide), nitrogen oxides (NOx), sulfur oxides (SOx), particulate matter (PM), and unburned hydrocarbons (HC). The amount and relative proportion of these pollutants varies according to the fuel-air mixture, compression ratio, injection timing, environmental conditions (e.g., atmospheric pressure, temperature, etc.), and the like. New stringent emission requirements like United States Environmental Protection Agency (EPA) Tier 4 locomotive (40 CFR Part 1033) emissions regulations drive the need of engine design methods that uses aftertreatment systems for controlling the exhaust emissions. However, the use of aftertreatment systems may increase the cost of manufacturing the engines and fuel consumption leading to high life cycle cost.
There is therefore a desire for a system and method for an enhanced technique for controlling exhaust emissions and achieving low specific fuel consumption of an engine.